Various materials such as metals, metal alloys and others can exhibit surface asperities such as rough features that are desirably smoothed. Many approaches have been implemented to reducing (the height of) surface asperities. Mechanical polishing has been used to physically remove material in the asperities. Non-contact polishing such as continuous-wave (CW) laser polishing and pulsed laser polishing (PLP) have also been used to reduce the surface roughness of metals and other materials. In CW laser polishing, portions of the surface are melted as the laser is scanned across the surface, and material can flow from asperities in the melted portions. In PLP, laser pulses irradiate the surface, melting the surface in a small area with each pulse. In these molten areas, surface asperities (protrusions from the surface) are regions of high surface tension and are thus “pulled down” in order to create lower surface tension. If this happens before resolidification, the resulting surface is smoother.
While these approaches have been useful, many aspects have remained challenging. For example, mechanical polishing removes material, which can be undesirable or wholly impractical. In CW polishing, melt depths and heat affected depths of 100s of microns can raise issues with underlying materials or components, and may not be suitable for devices with dimensions measured in 10s to 100s of microns. While PLP can provide better control of the melt depth and the resulting heat affected zone (HAZ), surface asperities remaining after polishing can be undesirably large.
These and other problems have been challenging to the reduction of surface asperities, and to doing so in micro-scale devices.